The following relates to the development of a laser-induced fluorescence imaging endoscope for mapping cancerous or precancerous tissues in hollow organs. In initial clinical studies, on colon polyps, Ultraviolet (UV) light was used at 370 nm to excite visible fluorescence (400-700 nm), the spectral signatures of which enabled differentiating between normal and abnormal tissues. Previously endoscopic imaging has been achieved using an optics module mounted in one of the biopsy ports of a two-port standard (white light) colonoscope. The optics module employs a quartz optical fiber and associated optics to deliver the UV light to the tissue, and a coherent quartz fiber-optic bundle to transmit the resulting fluorescence image to the proximal side of the endoscope, where a filter removes the large background of reflected UV light and the fluorescence image is then captured by a high-gain CID detector array.
Endoscopically-collected autofluorescence images of colonic mucosa can be used as a screening tool for detecting pre-cursors to colorectal cancer (CRC). Fluorescence has been used to distinguish between normal mucosa and adenomas. In particular, spectra measured with single point contact probes with the use of several different excitation wavelengths.
Fluorescence spectra have been obtained through optical fiber probes with several excitation wavelengths. An in vitro study performed a search over a wide range of excitation wavelengths, and concluded that 370 nm is optimal for distinguishing between normal mucosa and adenoma. Both in vitro and in vivo studies using adenomatous polyps as a model for dysplasia have shown that with this wavelength dysplasia has less peak intensity at 460 nm and may have increased fluorescence at 680 nm compared with normal colonic mucosa. Furthermore, the morphologic basis for these spectral differences has been studied by fluorescence microscopy. The decreased fluorescence intensity in polyps was attributed to its raised architecture, increased vasculature, and reduced collagen in the lamina propria. The red enhancements arise from increased fluorescence of the crypt cells, which may be caused by higher levels of porphyrin.